If you are configure a Cisco Pix or ASA device and you have a server on the inside interface and clients on the outside who are using PPTP to VPN into the network you must make sure you do the following things.
Allow GRE traffic in the security policy
Allow PPTP traffic in the security policy
static entry for pptp on 1723 to your server
run this command in configure mode “fixup protocol pptp 1723”